The present invention relates to an electrophotographic copier or similar image recording apparatus of the type having a developing unit which is replaceable with another for changing recording color.
In an electrophotographic copier, for example, an imagewise reflection from a document is focused onto a photoconductive element to form an electrostatic latent image thereon. The latent image is developed by a developing unit which stores a developer in the form of toner therein. More specifically, toner is deposited on the photoconductive element in association with the potential distribution of the latent image to produce a toner image. Recording color, therefore, can be changed by replacing the toner of particular color with toner of another color. A relatively inexpensive copier available today is operable with a plurality of developing units each storing toner of different color and being replaceable with each other to select desired recording color. A problem heretofore pointed out is that a change in the kind, particularly color, of toner to be used causes the individual recording characteristics to change with respect to various process factors, e.g. bias voltage for development, transfer current, amount of exposing light, and toner density. Since a desirable recording in unachievable unless optimum and accurately determined recording conditions are selected with respect to the above-mentioned process conditions, it is preferable that a change in color be accompanied by a change in process conditions.
For changing the recording conditions as stated above, it has been customary to install in each developing unit an exclusive mechanical part for the identification of toner color or to rely on operator's manipulations of a mode switch. A drawback with the extra mechanical part scheme is the complicated and expensive construction, and another drawback is that each developing unit storing toner of particular color should be provided with a different mechanical structure. On the other hand, the mode switch scheme is apt to invite erroneous manual operations which would render a recording incomplete and forces the operator to withstand troublesome operations for the confirmation of recording color.